Performance is an evolving target. Meta reported they spend ~0.05% (1 out of every 2000 CPU cycles) on X25519 key exchange within the last year, which is quite significant. If that can be brought down, that's worthwhile. And ongoing research and deployment of PQC will make key exchange even more expensive.

> If there is not some novel, brand new algorithm that is being employed, the answer is because it is insecure.

Lol that is just not true at all. A major point of discussion when NIST announced the SHA3 finalist being Keccak back in ~2012(?) was that BLAKE1 at the time offered significantly better software performance, which was considered an important practical reality, and was faster than SHA-2 at a higher (but insignificantly so) security margin; their own report admitted as much. The BLAKE1 family is still considered secure today, its internal HAIFA design is very close to existing known designs like Merkle–Damgård, it isn't some radically new thing.

So why did they pick Keccak? Because they figured that SHA-2 was plenty good and already deployed widely, so "SHA-2 but a little faster" was not as compelling as a standard that complimented it in hardware; they also liked Keccak's unique sponge design that was new and novel at the time and allowed AEAD, domain separation, etc. They admit ultimately any finalist including BLAKE would have been a good pick. You can go read all of this yourself. The Keccak team even has new work on more performant sponge-inspired designs, such as their work on Farfalle and deck functions.

The reality is that some standards are chosen for a bunch of reasons and performance is only one of them, though very important. But there's plenty of room for non-standard things, too.